Dude im in a black metal band called ShastaMcNasta and it basically just means we dont give a fuck . I honestly think Necromancer sounds ok and just ok. I dont think the name matters, as long as your tunes are cool.

i've gotten lots of laughs but lots of compliments at the same time...so i mean...i'm happy with it, people are just gonna have to ignore the fact that its from a game...even though any REAL fan of black metal that has a 360, HAS THAT GAME! XD but yeah I've got some sick musicians ready to work so we're gonna have some sick music, don't judge a band by it's name. =P

Not to be negative or anything but i think Necromancer is a bit cliché isn't it? Shegorath sounds better though, my opinion.

It's been taken anyways... if that matters.
I like really bleak black metal band names, (Dark Funeral for example.)
I do like your sheogorath name though. It works as a temporary... but you could do a bit better I think.
Either way, I hope it works out. I'm trying to start one myself.